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Abstract Thioredoxin reductase (TrxR), a major component of the thioredoxin system, makes a critical role in regulating cellular redox signaling and is found to be overexpressed in many human cancer cells. TrxR has become an attractive target for anticancer agents. In this work, three Ru(II) complexes with salicylate as ligand, [Ru(phen) 2 (SA)] (phen = 1,10-phenanthroline, SA = salicylate, 1), [Ru(dmb) 2 (SA)] (dmb = 4,4′-dimethyl-2,2′-bipyridine, 2) and [Ru(bpy) 2 (SA)] (bpy = 2,2′-bipyridine, 3), were synthesized and characterized. The anticancer effect exerted by them was evaluated. Complex 1 was found to exhibit obvious anticancer activity, in comparison with cisplatin, against cancer cell lines, while displaying low toxicity to the normal cell line BEAS-2B. The mechanism of complex 1 cancer cell growth suppress was investigated in A549 cells. Complex 1 exerted its anticancer through inducing apoptosis and triggering cell cycle arrest at the G0/G1 phase. Complex 1 can selectively inhibit TrxR activity and thus promote the generation and accumulation of reactive oxygen species (ROS), which subsequently trigger mitochondrial dysfunction and DNA damage, activate oxidative stress-sensitive mitogen activated protein kinase (MAPK), and suppress the protein kinase B (PKB or AKT) signal pathway, resulting in apoptosis in A549 cells. Graphical abstract The in vitro cytotoxicity and apoptosis-inducing mechanism of new synthetic Ru(II) salicylic acid complexes have been extensively explored by 3-(4,5-dimethylthiazole)-2,5-diphenyltetraazolium bromide (MTT) assay, flow cytometry, inverted fluorescence microscope as well as western blotting experimental techniques. The inhibition of thioredoxin reductase (TrxR) activity by Ru(II) complexes was also investigated. Unlabelled Image Highlights • Three new Ru(II) salicylic acid complexes were synthesized and characterized. • The Ru complexes present high selectivity between tumor cells and normal cells. • The Ru complexes could inhibit thioredoxin reductase (TrxR) activity. • The Ru(II) complexes could induce cellular reactive oxygen species (ROS) accumulation. • The cellular uptake, DNA damage and apoptosis-inducing mechanism were investigated. [ABSTRACT FROM AUTHOR]

Here we present the preparation of 14 pairs of cis - and trans -diammine monochlorido platinum(II) complexes, coordinated to heterocycles (i.e., imidazole, 2-methylimidazole and pyrazole) and linked to various acylhydrazones, which were designed as potential inhibitors of the selenium-dependent enzymes glutathione peroxidase 1 (GPx-1) and thioredoxin reductase 1 (TrxR-1). However, no inhibition of bovine GPx-1 and only weak inhibition of murine TrxR-1 was observed in in vitro assays. Nonetheless, the cis configured diammine monochlorido Pt(II) complexes exhibited cytotoxic and apoptotic properties on various human cancer cell lines, whereas the trans configured complexes generally showed weaker potency with a few exceptions. On the other hand, the trans complexes were generally more likely to lack cross-resistance to cisplatin than the cis analogues. Platinum was found bound to the nuclear DNA of cancer cells treated with representative Pt complexes, suggesting that DNA might be a possible target. Thus, detailed in vitro binding experiments with DNA were conducted. Interactions of the compounds with calf thymus DNA were investigated, including Pt binding kinetics, circular dichroism (CD) spectral changes, changes in DNA melting temperatures, unwinding of supercoiled plasmids and ethidium bromide displacement in DNA. The CD results indicate that the most active cis configured pyrazole-derived complex causes unique structural changes in the DNA compared to the other complexes as well as to those caused by cisplatin, suggesting a denaturation of the DNA structure. This may be important for the antiproliferative activity of this compound in the cancer cells. [ABSTRACT FROM AUTHOR]

We report the application of cationic tri- and tetra-nuclear gold(I) phosphine complexes [Au 3 (μ-dppen) 3 ]X 3 and [Au 4 (μ-dppa) 4 ]X 4 (X = OTf, PF 6 ) [OTf = trifluoromethanesulfonate, dppen = trans -1,2-bis(diphenylphosphino)ethene, dppa = bis(diphenylphosphino)acetylene] for cancer treatment. The results of cytotoxicity tests on four different cancer cells [prostate (DU145), cervical (HeLa), breast (MDAMB-231) and fibro sarcoma (HT1080)] indicate these complexes possess remarkable tumor cell growth inhibitory effects and high selectivity towards cancer cells. The anti-tumor mechanism of the tri- and tetra-nuclear gold(I) complexes has also been investigated. [ABSTRACT FROM AUTHOR]

The alkynyl gold(I) derivative [Au(C≡CPh)(PTA)] (PTA = 1,3,5-triaza-7-phosphaadamantane) induces apoptosis in colorectal carcinoma tumour cells (Caco-2) without affecting to normal enterocytes. [Au(C≡CPh)(PTA)] is a slight lipophilic drug, stable in PBS (Phosphate Buffered Saline) and able to bind BSA (Bovin Serum Albumin) by hydrophobic interactions. Once inside the cell, [Au(C≡CPh)(PTA)] targets seleno proteins such as Thioredoxin Reductase 1, increasing ROS (Reactive Oxygen Species) levels, reducing cell viability and proliferation and inducing mitochondrial apoptotic pathway, pro-apoptotic and anti-apoptotic protein imbalance, loss of mitochondrial membrane potential, cytochrome c release and activation of caspases 9 and 3. Moreover, unlike other metal-based drugs such as cisplatin , [Au(C≡CPh)(PTA)] does not target nucleic acid, reducing the risk of side mutation in the DNA. In consequence, our results predict a promising future for [Au(C≡CPh)(PTA)] as a chemotherapeutic agent for colorectal carcinoma. [ABSTRACT FROM AUTHOR]

This paper reports the inhibitory effect on the cytosolic thioredoxin reductase (TrxR1) in vitro by the ansa-ferrocifen derivative (ansa-FcdiOH, 1 ). We found that 1 decreased only slightly enzyme activity (IC 50 = 8 μM), while 1* , the species generated by enzymatic oxidation by the HRP (horseradish peroxidase)/H 2 O 2 mixture, strongly inhibited TrxR1 (IC 50 = 0.15 μM). At the same concentrations, neither 1 nor 1* had effect on glutathione reductase (GR). The most potent TrxR1 inhibitor did not appear to be the corresponding quinone methide as it was the case for ferrocifens of the acyclic series, or the stabilized carbocation as in the osmocifen series, but rather the quinone methide radical. This hypothesis was confirmed by ab-initio calculations of the species generated by oxidation of 1 and by EPR spectroscopy. BIAM (biotin-conjugated iodoacetamide) assay showed that 1* targeted both cysteine and selenocysteine of the C-terminal redox center of TrxR1. [ABSTRACT FROM AUTHOR]

The synthesis and the biological effects of two ferrocifen analogs in the osmium series, namely the monophenolic complex 1 , the tamoxifen-like complex 2 and their oxidized quinone methide (QM) derivatives, 1-QM and 2-QM , are reported. Inhibition of purified thioredoxin reductase (TrxR) is observed with 1 and 2 only after their enzymatic oxidation by the hydrogen peroxide/horseradish peroxidase (H 2 O 2 /HRP) system with IC 50 of 2.4 and 1.2 μM respectively. However, this inhibition is larger than that obtained with the corresponding quinone methides (IC 50 = 5.4 μM for 1-QM and 3.6 μM for 2-QM ). The UV–Vis spectra of 1 or 2 incubated in the presence of H 2 O 2 /HRP show that the species generated is not a quinone methide, but probably the corresponding cation. In Jurkat cells, 2 shows high toxicity (IC 50 = 7.4 μM), while 1 is less effective (IC 50 = 42 μM). Interestingly, a significant inhibition of TrxR activity is observed in cells incubated with 2 (about 70% inhibition with 15 μM) while the inhibition induced by 1 is much weaker (about 30% inhibition with 50 μM). This strong inhibition of TrxR by 2 leads to accumulation of thioredoxin and peroxiredoxin 3 in oxidized form and to a decrease of the mitochondrial membrane potential (MMP). These results show that cytotoxicity of the osmocifens depends on their oxidation within the cell and that inhibition of thioredoxin reductase by oxidized species is a key factor in rationalizing the cytotoxicity of these complexes on Jurkat cells. [ABSTRACT FROM AUTHOR]

Three new compounds containing the bis(triphenylphosphane)iminium cation (PPN + ) with ClO 4 − , BF 4 − and [AgCl 2 ] − as counter anions have been synthesized and structurally characterized. The two derivatives with ClO 4 − and BF 4 − were found to be isostructural by single crystal X-ray diffraction. Interestingly, the three compounds show extremely potent antiproliferative effects against the human cancer cell line SKOV3. To gain insights into the possible mechanisms of biological action, several intracellular targets have been considered. Thus, DNA binding has been evaluated, as well as the effects of the compounds on the mitochondrial function. Furthermore, the compounds have been tested as possible inhibitors of the seleno-enzyme thioredoxin reductase. [ABSTRACT FROM AUTHOR]

Gold(I) complexes are an important tool in the arsenal of established approaches for treating rheumatoid arthritis (RA), while some recent studies have suggested that gold nanoparticles (Au NPs) may also be therapeutically efficacious. These observations prompted the current biological studies involving gold(I) anti-RA agents and Au NPs, which are aimed towards improving our knowledge of how they work. The cytotoxicity of auranofin, aurothiomalate, aurothiosulfate and Au NPs towards RAW264.7 macrophages was evaluated using the MTT assay, with the former compound proving to be the most toxic. The extent of cellular uptake of the various gold agents was determined using graphite furnace atomic absorption spectrometry, while their distribution within macrophages was examined using microprobe synchrotron radiation X-ray fluorescence spectroscopy. The latter technique showed accumulation of gold in discrete regions of the cell, and co-localisation with sulfur in the case of cells treated with aurothiomalate or auranofin. Electrospray ionization mass spectrometry was used to characterize thioredoxin reductase (TrxR) in which the penultimate selenocysteine residue was replaced by cysteine. Mass spectra of solutions of TrxR and aurothiomalate, aurothiosulfate or auranofin showed complexes containing bare gold atoms bound to the protein, or protein adducts containing gold atoms retaining some of their initial ligands. These results support TrxR being an important target of gold(I) drugs used to treat RA, while the finding that Au NPs are incorporated into macrophages, but elicit little toxicity, indicates further exploration of their potential for treatment of RA is warranted. [ABSTRACT FROM AUTHOR]

Abstract: Gold-based drugs typically behave as strong inhibitors of the enzyme thioredoxin reductase (hTrxR), possibly as the consequence of direct Gold(I) coordination to its active site selenocysteine. To gain a deeper insight into the molecular basis of enzyme inhibition and prove gold-selenocysteine coordination, the reactions of three parent Gold(I) NHC compounds with the synthetic C-terminal dodecapeptide of hTrxR containing Selenocysteine at position 498, were investigated by electrospray ionization mass spectrometry (ESI-MS). Formation of 1:1 Gold-peptide adducts, though in highly different amounts, was demonstrated in all cases. In these adducts the same [Au-NHC]+ moiety is always associated to the intact peptide. Afterward, tandem MS experiments, conducted on a specific Gold-peptide complex, pointed out that Gold is coordinated to the selenolate group. The relatively large strength of the Gold-selenolate coordinative bond well accounts for potent enzyme inhibition typically afforded by these Gold(I) compounds. In a selected case, the time course of enzyme inhibition was explored. Interestingly, enzyme inhibition turned out to show up very quickly and reached its maximum just few minutes after mixing. Overall, the present results offer some clear insight into the process of thioredoxin reductase inhibition by Gold-based compounds. [Copyright &y& Elsevier]

Abstract: Biological properties of a series of aminophosphine-thiolate gold(I) complexes [Au(SR)(PPh2NHpy)] [Ph2PNHpy=2-(diphenylphosphinoamino)pyridine; HSR=2-mercaptopyridine (2-HSpy) (3), 2-mercaptonicotinic acid (2-H2-mna) (4), 2-thiouracil (2-HTU) (5) or 2-thiocytosine (2-HTC) (6)] and [Au(SR){PPh2NH(Htrz)}] [Ph2PNH(Htrz)=3-(diphenylphosphinoamino)-1,2,4-triazole]; HSR=2-mercaptopyridine (2-HSpy) (7), 2-thiocytosine (2-HTC) (8) or 6-thioguanine (6-HTG) (9) have been studied. Their antitumor properties have been tested in vitro against two tumor human cell lines, HeLa (derived from cervical cancer) and MCF-7 (derived from breast cancer), using a metabolic activity test (3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide, MTT). Some of them showed excellent cytotoxic activity. With the aim to obtain more information about the mechanisms of action of these derivatives, the interactions of complexes 3, 5, 7 and 9 with thioredoxin reductase in HeLa cells were studied. They showed a potent inhibition of thioredoxin reductase activity. In order to complete this study, interactions of the complexes with calf thymus (CT-) DNA and with different bacterial DNAs, namely the plasmid pEMBL9 and the promoter region of the furA (ferric uptake regulator A) gene from Anabaena sp. PCC 7120 were investigated. Although interactions of complexes with CT-DNA have been verified, none of them cause significant changes in its structure. [Copyright &y& Elsevier]

Abstract: Lanthanum chloride (LaCl3) is a good inhibitor of both the cytosolic and mitochondrial thioredoxin reductase with IC50 values of 1.75 and 7.46μM, respectively. On the contrary, the related enzyme glutathione reductase is not inhibited by lanthanum ions even at relatively high concentrations. In the presence of LaCl3, steady-state kinetics shows a non-competitive type of inhibition with 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) as a substrate suggesting no interaction of this ion with the thiol/selenol active site of thioredoxin reductase. Comparison of the electrostatic surface potential of thioredoxin reductase shows that the presence of a trivalent cation such as La3+ decreases the negatively charged area of the enzyme surface particularly in the region closed to the NADPH binding site. Human ovarian carcinoma cells (A2780 cells) incubated with lanthanum ions show a noticeable inhibition of thioredoxin reductase activity indicating the ability of this ion to reach the active site of the enzyme even in a cellular setting. In addition, A2780 cells treated with LaCl3 show an increase in reactive oxygen species production in part dependent on thioredoxin reductase inhibition. [Copyright &y& Elsevier]

Abstract: Complexes [Au(H2Ac4DH)Cl]∙MeOH (1) [Au(H22Ac4Me)Cl]Cl (2) [Au(H22Ac4Ph)Cl]Cl∙2H2O (3) and [Au(H22Bz4Ph)Cl]Cl (4) were obtained with 2-acetylpyridine thiosemicarbazone (H2Ac4DH), its N(4)-methyl (H2Ac4Me) and N(4)-phenyl (H2Ac4Ph) derivatives, as well as with N(4)-phenyl 2-benzoylpyridine thiosemicarbazone (H2Bz4Ph). The compounds were cytotoxic to Jurkat (immortalized line of T lymphocyte), HL-60 (acute myeloid leukemia), MCF-7 (human breast adenocarcinoma) and HCT-116 (colorectal carcinoma) tumor cell lines. Jurkat and HL-60 cells were more sensitive than MCF-7 and HCT-116 cells. Upon coordinating to the gold(I) metal centers in complexes (2) and (4), the cytotoxic activity of the H2Ac4Me and H2Bz4Ph ligands increased against the HL-60 and Jurkat tumor cell lines. 2 was more active than auranofin against both leukemia cells. Most of the studied compounds were less toxic than auranofin to peripheral blood mononuclear cells (PBMC). All compounds induced DNA fragmentation in HL-60 and Jurkat cells indicating their pro-apoptotic potential. Complex (2) strongly inhibited the activity of thioredoxin reductase (TrxR), which suggests inhibition of TrxR to be part of its mechanism of action. [Copyright &y& Elsevier]

The effects of gold(I) complexes (auranofin, triethylphosphine gold and aurothiomalate), gold(III) complexes ([Au(2,2′-diethylendiamine)Cl]Cl2, [(Au(2-(1,1-dimethylbenzyl)-pyridine) (CH3COO)2], [Au(6-(1,1-dimethylbenzyl)-2,2′-bipyridine)(OH)](PF6), [Au(bipydmb-H)(2,6-xylidine)](PF6)), metal ions (zinc and cadmium acetate) and metal complexes (cisplatin, zinc pyrithione and tributyltin) on mitochondrial thioredoxin reductase and mitochondrial functions have been examined. Both gold(I) and gold(III) complexes are extremely efficient inhibitors of thioredoxin reductase showing IC50 ranging from 0.020 to 1.42 μM while metal ions and complexes not containing gold are less effective, exhibiting IC50 going from 11.8 to 76.0 μM. At variance with thioredoxin reductase, auranofin is completely ineffective in inhibiting glutathione peroxidase and glutathione reductase, while gold(III) compounds show some effect on glutathione peroxidase. The mitochondrial respiratory chain is scarcely affected by gold compounds while the other metal complexes and metal ions, in particular zinc ion and zinc pyrithione, show a more marked inhibitory effect that is reflected on a rapid induction of membrane potential decrease that precedes swelling. Therefore, differently from gold compounds, the various metal ions and metal complexes exert their effect on different targets indicating a lower specificity. It is concluded that gold compounds are highly specific inhibitors of mitochondrial thioredoxin reductase and this action influences other functions such as membrane permeability properties. Metal ions and metal complexes markedly inhibit the activity of thioredoxin reductase although to an extent lower than that of gold compounds. They also inhibit mitochondrial respiration, decrease membrane potential and, finally, induce swelling. [Copyright &y& Elsevier]

The objective of this work was to determine whether long-term selenium (Se) deficiency might affect the antioxidant capacity of rat aorta, and the activities and expressions of glutathione peroxidase (GPx) and thioredoxin reductase (TR) in rat arterial walls. Weanling male Wister rats were fed Se-deficient or Se-adequate diets for 12 months. For the Se supplementation, sodium selenite was supplemented in drinking water (1 μg Se/ml) for 1 month. The aorta isolated from these groups were used to determine activities and mRNA levels. In comparison with the control, the activity and expression of GPx, superoxide dismutase activity and the total antioxidant capacity were significantly decreased in Se-deficient rats arterial walls. Following Se supplementation, they were restored to different extents. The content of malondialdehyde was increased markedly in Se-deficient rats. There seems an inverse relationship between the dietary Se and the activity and expression of TR. A positive relationship exists between dietary Se and the antioxidant capacity of rat arterial walls. The activities and expressions of GPx and TR in arterial walls were regulated by selenium by different mechanisms. Regulation of the expression of TR was mediated by reactive oxygen species, but of GPx by selenium status. The thioredoxin system may be the major cellular redox signaling system in rat arteries, rather than the glutathione system. [Copyright &y& Elsevier]

Metal complexes of N-heterocyclic carbene (NHC) ligands are the object of increasing attention for therapeutic purposes. Among the different metal centres, interest on Au-based compounds started with the application as anti-arthritis drugs. On the other hand, Ag(I) antimicrobial properties have been known for a long time. For Au(I)/Au(III)-NHC and Ag(I)-NHC anti-tumour and anti-proliferative properties have been quite recently demonstrated. In addition to these and as for Group 11, copper is a much less investigated metal centre, but a few papers underline its pharmacological potential. This review wants to focus on the different biological targets for these metal-based compounds. It is divided into chapters which are respectively devoted on: i) mitochondria and thiol oxidoreductase systems; ii) other relevant enzymes; iii) nucleic acids. Examples of representative coinage NHCs for each of the targets are provided together with significant references on recent advances on the topic. Moreover, a final comment summarises the aspects enlightened by each chapter and provides some hints to better understand the metal-NHCs mechanistic behaviour based on structure-activity relationships. N-heterocyclic carbene ligands find application as potential anticancer compounds, and group 11 metal complexes give very promising results. This review is divided into Chapters which focus on the targets for the probe. The researcher finds information for directing it towards mitochondria and thiol oxidoreductase systems, other enzymes or nucleic acids. [Display omitted] • Cellular targets for N-heterocyclic carbenes (NHCs) metal-complexes are reviewed. • For each target, representative Au(I)/Au(III)/Ag(I)/Cu(II)-NHCs are presented. • The modes-of-action are described at a molecular level. • Structure-activity relationships are elucidated. [ABSTRACT FROM AUTHOR]

The antiproliferative properties of a series of structurally-related gold(I) and silver(I) linear complexes inspired to the clinically established gold-based drug auranofin were investigated in A2780 ovarian cancer cells and in their auranofin (A2780/AF-R) and cisplatin (A2780/CDDP-R) resistant counterparts. In A2780 cells and in the cisplatin-resistant subline, gold-based analogues manifested a cytotoxicity profile comparable or superior to auranofin, while the silver-based analogues were less active; both gold and silver complexes overcame cisplatin resistance. Yet, a high degree of cross resistance toward gold analogues was noticed in A2780/AF-R cells. In the same cell line cross-resistance for silver analogues was also observed, though lower. All metal complexes were scrutinized for their ability to inhibit thioredoxin reductase (TrxR), the putative primary target for auranofin: overall, gold compounds were more potent TrxR inhibitors than the corresponding silver compounds, probably, as the consequence of the stronger binding of gold to the active site selenocysteine residue. These results highlight that the thiosugar ligand of auranofin is not essential for cytotoxicity while the nature of the metal center (gold/silver) plays a relevant role in its modulation. In addition, a rather clear correlation was found between cytotoxic potency of tested compounds and their ability to inhibit TrxR activity, being gold compounds more effective than silver analogues. However, the residual TrxR activity, measured in A2780 cells treated with the half-maximal inhibitory concentrations of various metal complexes, resulted far higher than expected. These results suggest that additional cytotoxic mechanisms must be operative. The implications of these results are discussed. The graphical abstract reports the chemical structures of study gold(I) and silver (I) complexes, the outline of the performed biological studies and the correlations among cytotoxic activity, thioredoxin reductase (TrxR) activity in cell extracts, percent cellular TrxR activity for each metal compound in the A2780 human ovarian cancer cell line. Unlabelled Image • The cytotoxicity of gold(I) and silver(I) auranofin analogues was investigated. • Both gold and silver complexes overcome resistance to cisplatin. • The thiosugar ligand of auranofin is not essential for the cytotoxic activity. • The nature of the metal center plays a relevant role in cytotoxicity modulation. • Inhibition of thioredoxin reductase activity by gold and silver complexes was studied. [ABSTRACT FROM AUTHOR]

The application of gold as drug candidate dated back to 2500 BC and its relevance in medicine became more appealing following 1985 FDA approval of ingested Auranofin for the treatment of rheumatoid arthritis. In this study, we have provided a density functional theory (DFT) study of some gold(III)-dithiocarbamate complexes with characteristic anticancer potentials. DFT calculation of the reactivity and selectivity properties of these complexes with an enzyme template of thioredoxin reductase (TrxR) was carried out. The investigation proceeds with theoretical characterization of the selected compounds through spectroscopic analyses. IR and UV–vis analyses were carried out and the calculated values are comparable to experimental results. NMR assignment was determined for the gold compounds and the estimated theoretical chemical shift values agree with available experimental data from literature. The obtained DFT-based chemical parameters proved to be significant in evaluating the selectivity, reactivity and stability of the gold(III) complexes as potential anticancer moieties, specifically against TrxR. Calculated binding free energy gave similar order with the available in vitro inhibition profile of these gold(III)-dithiocarbamate complexes against TrxR. The outcome of this DFT study could serve as a useful guide towards future design of new and potent anticancer drug candidate. The investigated chemical reactivity properties could be considered and applied to a wide range of bioactive compounds and enzyme—inhibitor systems. Density functional theory investigation of gold(III)-dithiocarbamate compounds: characterization and reactivity prediction. Unlabelled Image • Characterization of gold(III)-dithiocarbamate complexes was done theoretically. • Density functional theory calculated spectroscopic data agree with experimental results. • Gold(III)-dithiocarbamate complexes was proposed to be potential anticancer moieties. • The complexes were noted to target thioredoxin reductase (TrxR) with ample reactivity. • The outcome of this study could serve as a useful guide in anticancer drug design. [ABSTRACT FROM AUTHOR]

A silver(I) and a gold(I) complex of the fluorescent N-heterocyclic carbenic (NHC) ligand 1-(9-anthracenylmethyl)-3-(3-trimethylsilyl-2-propynil)-benzimidazol-2-ylidene have been synthesized and characterized. These compounds show cytotoxicity in the micromolar range and higher antiproliferative properties than cisplatin (CDDP) against several tumour cell lines such as SW480 (colon), A549 (lung) and HepG2 (liver). Both metal complexes are successfully internalized by SW480 cells being the silver compound the most accumulated. Subsequently, they were evaluated as inhibitors of the selenoenzyme Thioredoxin reductase (TrxR) and as DNA binders. Fluorescence microscopy confirmed that both protein and DNA binding could be involved in the biological activity of the compounds. The silver carbene was the most effective enzyme inhibitor with an IC 50 in the nanomolar range. Also, interaction studies with natural double stranded DNA highlight a strong stabilisation of the double helix after binding to the Ag(I) carbene, indicating its potential suitability as dual-targeting anticancer active molecule. We have studied the silver(I) and gold(I) complexes of an N-heterocyclic carbenic (NHC) ligand, further functionalised with an anthracenyl moiety. They were found to be active multitarget compounds. The metal centre tunes the biological features: Ag(I)-NHC intercalates into DNA and Au(I)-NHC does not. Further mechanistic aspects are discussed. Unlabelled Image • The potential of Ag(I)/Au(I)-N-heterocyclic carbenes (NHC) complexes is evidenced. • Both complexes enter cancer cells (>cisplatin), Ag(I)-NHC is highly accumulated. • Both inhibit rat liver purified thioredoxin reductase, Ag(I)-NHC is more potent • Ag(I)-NHC undergoes hydrolysis and very strongly stabilises natural DNA. • Au(I)-NHC is not hydrolysed, weakly binds DNA but is still cytotoxic. [ABSTRACT FROM AUTHOR]

A series of phosphino-thiosemicarbazone gold(I) dinuclear complexes obtained by two different synthetic procedures have been prepared. All the compounds have been spectroscopically characterized including single crystal X ray diffraction analysis in some of cases. [Au 2 (HL 1 )Cl 2 (1), [Au 2 (HL 2 ) 2 Cl 2 (2) and [Au 2 (HL 3 ) 2 Cl 2 (3) have been prepared by chemical synthesis using a gold(III) salt as precursor; while [Au 2 (L 1 ) 2 (4), [Au 2 (L 2 ) 2 ∙2CH 3 CN (5) and [Au 2 (L 3 ) 2 (6) have been isolated from an electrochemical synthesis (HLn = 2-[2-(diphenylphosphanyl)-benzylidene]- N -R-thiosemicarbazone; HL1: R = methyl, HL2: R = methoxyphenyl, HL3: R = nitrophenyl). The in vitro cytotoxic activity of these gold(I) complexes was tested against some human tumor cell lines: HeLa 229 (cervical epithelial carcinoma), MCF-7 (ovarian adenocarcinoma), NCI-H460 (non-small-cell lung cancer) and MRC5 (normal human lung fibroblast), and the IC 50 values compared with those of cisplatin. The neutral methyl-substituted complexes 1 and 4 and methoxyphenyl 5 displayed significant cytotoxic activities in all investigated cancer cell lines, being 1 and 4 the most effective. The ability of complexes 1 and 4 to induce cell death by apoptosis in Hela 229 was also investigated by fluorescence microscopy using the apoptotic DNA fragmentation as marker. These results indicated that the inhibition of cell proliferation is mainly due to an apoptotic process. In order to obtain more information about the mechanism of action of these metallocompounds, the interactions of complexes 1 and 4 with the thioredoxin reductase (TrxR) enzyme were analyzed. Both complexes exhibited a strong inhibition of the thioredoxin reductase activity. Unlabelled Image • Gold(I) complexes obtained by traditional and a electrochemical procedures were studied. • Electrochemical synthesis makes available a new arsenal of neutral gold(I) compounds. • Complexes containing the methyl group are the most cytotoxic against the investigated cancer cell lines. • These complexes exhibit a strong inhibition of the thioredoxin reductase activity. [ABSTRACT FROM AUTHOR]